Interestingly, the slowest-performing add-on they show is the well-respected and popular Firebug, which adds 75% to the start-up time. I expected to see some low-quality add-on at the top. I don't think they're going to drop a banhammer on slow add-ons with Firebug at the top of the list. More listed here: https://addons.mozilla.org/en-US/firefox/performance/
I wish that list wouldn't be about a metric I couldn't care less about but unfortunately everyone else seems to only care about start up time :(
I don't see many people failing to realise this. Also I think most people close their browsers from time to time, even if most people on HN don't. (I've heard rumours that some people even turn their computers off at night.) These people care about start-up time.
Does the average person actually shut down to the point of doing a cold boot the next day? I have the impression most just tap the power button (which hibernates to disk by default), or else simply walk away and let this happen automatically.
I have one non-tech-savvy friend who just holds his laptop's power button down for 5 seconds when he's done using it. "Oh yeah, it's great, it shuts down properly and instantly and I never lose any data!" I had to emphatically explain to him that he was effectively playing Russian roulette with his life's work. This is just an anecdote, but while anecdotes cannot set averages, they can be used to find a lower bound on extremes.